BSD is not Linux. They look similar, as they are both "Unix-like" but they are not the same. In this instance, the init(8) on OpenBSD is only executed by the kernel, not by an administrative command. As described in the init(8) man page, klll(1) may be used to signal init to terminate multi-user state and resume in single-user mode.

It is not the same program as the Linux init program.

On OpenBSD, you restart or halt with reboot(8) or halt(8) and you may, if you ever have multiple shell users, use shutdown(8) to notify users and manage timing of restart or halt execution.